The present invention relates to an elevator guide shoe as defined in the preamble of claim 1.
A guide shoe is used in an elevator car to guide it along guide rails in an elevator shaft. The guide shoe is provided with bearing elements based on a sliding or rolling action, which rest against the guide rails. However, a car mounted with such bearings on the guide rails produces a noise when moving, which is propagated as structure-borne noise to the inside of the car. Such noise is unpleasant for the passengers and reduces the level of comfort they experience in using the elevator.
In prior art, several methods have been used to eliminate these problems. In Japanese patent specification 7196273, these problems are dealt with by using servo-controlled magnetic coils to float the car. This is a very difficult solution in respect of the control engineering system involved and therefore expensive.
Japanese patent specification 55-25589 presents an elevator which uses permanent magnets fitted in the elevator shaft and permanent magnet guides fitted close to them on the elevator car. The elevator car is supported in a floating manner based on magnetic repulsion between the permanent magnet guides and guide rails. This is a difficult and expensive solution. Moreover, the long magnetic guide rail needed in the elevator shaft in this solution attracts all sorts of rubbish.
The object of the present invention is to eliminate the drawbacks described above. A specific object of the present invention is to disclose a new type of guide shoe that, being simple and reliable in construction, effectively damps the sound waves generated in the guide rail and guide shoe and prevents them from being propagated to the elevator car, thus making the elevator more agreeable to use.
As for the features characteristic of the invention, reference is made to the claims.
The guide shoe of the invention comprises a supporting frame attached to the elevator car and guides resting against guide rails in the elevator shaft. The guides used may consist of various known bearing elements mainly based on a sliding or rolling action. According to the invention, the guide shoe comprises an intermediate frame to which the guides are attached, the supporting frame and the intermediate frame being provided with permanent magnets appropriately disposed oppositely to each other to maintain a horizontal distance between the supporting frame and the intermediate frame, i.e. to keep them apart so that there is no direct contact between them. Thus, the supporting frame and the intermediate frame do not touch each other in the horizontal direction but are always separated by an air gap. Moreover, according to the invention, the supporting frame and the intermediate frame are connected to each other in the vertical direction by a suspension system that damps sound waves propagating via the structures.
In a preferred embodiment of the invention, the supporting frame consists of a box open on one of its lateral sides, the intermediate frame being fitted inside the box. The intermediate frame meets the guide rail in the direction of the open side of the supporting frame. The intermediate frame may be a body of e.g. U-shaped or semicircular form, surrounding the guide rail substantially on three sides of the rail.
The vertical suspension between the supporting frame and the intermediate frame preferably consists of an elastic suspension system that permits slight movements between the intermediate frame and the supporting frame relative to each other in both horizontal and vertical directions. Further, the suspension is preferably implemented using structures or materials with a low sound transmission capability to prevent the propagation of the noise generated between the guides and the guide rail to the elevator car.
The suspension may be implemented using e.g. suitable spiral springs and suspension cables connected to them, which may additionally comprise auxiliary structures inhibiting sound propagation. The elastic suspension may also be implemented using support blocks, pillows or jackets made e.g. of cork, fitted between the supporting frame and the intermediate frame.
In an embodiment of the invention, the guide shoe is provided with a detector for measuring the displacement between the supporting frame and the intermediate frame. The displacement may be relatively large e.g. when the car has a very eccentric load, and in this case the guide shoe is preferably provided with servo-connected electromagnets, which can be used to compensate undesirable displacements between the supporting frame and the intermediate frame.
Magnets of square or circular cross-section are ill suited for bidirectional magnetic floating because they always have a considerable parasitic spring constant perpendicular to the main springing direction. This parasitic spring constant should be focused in the direction in which the movement is mechanically restricted. For this reason, the permanent magnets used are preferably magnets having an elongated cross-section such that, of the edges perpendicular to the magnetising direction, i.e. the main springing direction, the horizontal edge is considerably longer than the vertical edge. Thus, the permanent magnet used here is an elongated permanent magnet bar whose magnetic poles are located on its opposite long sides.
The suspension system preferably comprises a plurality of horizontal permanent magnet bars placed side by side and in parallel directions at a vertical distance from each other. Thus, both the intermediate frame and the supporting frame have an equal number of equally sized elongated horizontal permanent magnet bars, the oppositely placed permanent magnet bars in the supporting frame and intermediate frame forming pairs of permanent magnets repellent to each other.
Preferably both the supporting frame and the intermediate frame are provided with a ferromagnetic backing to which the permanent magnets are fixed or on which they are supported. In this way, the height of the magnets, i.e. the dimension in the main springing direction can be halved while the field remains about the same.
As to their polarities, the permanent magnet pairs are preferably so arranged that adjacent permanent magnet pairs are of opposite polarity. This provides a considerable advantage because the crosswise force with the next pair is also a repulsive force, thus increasing the spring constant instead of reducing it as it would in the case of homopolar neighbours.
The permanent magnet pairs are preferably so disposed that they form a 180xc2x0 arch around the guide rail, i.e. so that the repulsive forces of the permanent magnet pairs from two opposite directions cancel each other while in the perpendicular horizontal direction between these the repulsive forces of the permanent magnet pairs press the intermediate frame against the guide rail in the elevator shaft.
The guide shoe of the invention has considerable advantages as compared with prior art. The invention provides a simple and cheap method of preventing the structure-borne noise in elevator guide rails from being transmitted to the elevator car. The elevator shaft need not be equipped with long magnetised guide rails and the structure does not necessarily require any regular adjustment. The invention makes it possible to achieve an elevator without a rigid mechanical connection between the guide rails and the elevator car, which would constitute a path for the transmission of sound waves between them. Thus, more noiseless and agreeable elevator travel is achieved.